Mapping stars and gas in nearby galaxies is fundamental for understanding their growth and the impact of their environment. This issue is addressed by comparing the stellar "edges" of galaxies Dₛₜₑₗₗₐᵣ, defined as the outermost diameter where in situ star formation significantly drops, with the gaseous distribution parameterized by the neutral atomic hydrogen diameter measured at 1 Mₛᵤₙ/pc², DHI. By sampling a broad HI mass range 10⁵ Mₛᵤₙ < MHI < 10¹¹ Mₛᵤₙ, we find several dwarf galaxies with MHI < 10⁹ Mₛᵤₙ from the field and Fornax Cluster which are distinguished by Dₛₜₑₗₗₐᵣ >> DHI. For the cluster dwarfs, the average HI surface density near Dₛₜₑₗₗₐᵣ is ~0.3 Mₛᵤₙ/pc², reflecting the impact of quenching and outside-in gas removal from ram pressure and tidal interactions. In comparison, Dₛₜₑₗₗₐᵣ/DHI ranges between 0.5-2 in dwarf field galaxies, consistent with the expectations from stellar feedback. Only more massive disk galaxies in the field can thus be characterized by the common assumption that Dₛₜₑₗₗₐᵣ DHI. We discover a break in the Dₛₜₑₗₗₐᵣ-Mₛₜₑₗₗₐᵣ relation at mbreak ~ 4×10⁸ Mₛᵤₙ that potentially differentiates the low mass regime where the influence of stellar feedback and environmental processes more prominently regulates the sizes of nearby galaxies. Our results highlight the importance of combining deep optical and HI imaging for understanding galaxy evolution.
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Chamba et al. (2024) studied this question.
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